In order for turbine operators and/or control systems to optimize overall system performance across competing demands of emissions levels, power output, and engine life, maximum information about each component's health and performance is needed. One key issue that has emerged in combustion systems is that of combustion instabilities—that is, self-excited, combustion driven oscillations that generally occur at discrete frequencies associated with the combustor's natural acoustic modes. Minimizing the amplitude of these oscillations is essential for maximizing hot section part life—however, tradeoffs between dynamics amplitude, emissions, and power output are routinely encountered.
Currently, when turbines are being commissioned or simply going through day to day operation, the operator has no idea how the stability of the system is affected by changes to fuel splits/operating conditions unless, of course, the system actually becomes unstable.
Johnson et al. pursued an analysis technique for determine stability margin quantifications in a publication entitled “Experimental Determination of the Stability Margin of a Combustor Using Exhaust Flow and Fuel Injection Rate Modulations” presented at the Proceedings of the Combustion Institute, Vol. 28, 2000. Their technique required, however, a pulsing fuel injector and acoustic driver. Such external actuation is not a practical practice for operating combustors in day to day operations. As such, this technique may be useful in a lab setting but is not practical for a fielded system.
Hobson et al also attempted to infer combustor damping by monitoring the bandwidth of pressure or compressor casing vibration in a publication entitled “Combustion Instabilites in Industrial Gas Turbines—Measurements on Operating Plant and Thermoacoustic Modeling” as presented to the International Gas Turbine & Aeroengine Congress & Exhibition in June of 1999. However, the use of frequency domain techniques to determine damping are much more susceptible to noise and less robust than those described here.
Thus, there exists a need in the industry for a system and method to provide the combustor operator a quantitative description of how near a combustor is to its stability boundary, so that the user can determine whether small changes in fuel splits, operating or ambient conditions are likely to effect combustor dynamics.